Following a unilateral lesion of the rat nucleus basalis of Meynert, there was an acute (1 week) increase in the number of neocortical M2 muscarinic binding sites which-returned to normal after 3 months. Neocortical Ml muscarinic binding sites were normal at 1 week but decreased at 3 months. These changes were bilateral and suggest that bilateral changes in cortical cholinergic receptors follow unilateral degeneration of cholinergic input. Differentiation of adrenergic derivatives of the rat neural crest was examined using the glucocorticoid receptor (GR) as a molecular marker. Both adrenal and extra-adrenal chromaffin cells had similar temporal patterns of GR localization and responsiveness to dexamethasone during postnatal development, whereas these same characteristics were not found in sympathetic neurons. The numerial increase in extra-adrenal chromaffin cells in the aging rat was not accompanied by a cellular proliferation mechanism. Nerve growth factor (NGF) receptors were identified in the human cerebral cortex and had a dissociation constant (Kd) of 150-300 pM. The binding of [125I]-NGF to membranes prepared from Alzheimer's disease brains did not differ significantly from binding in normal brains. Receptor binding did not reflect the laminar distribution of cortical cholinergic markers,suggesting that the NGF receptors are not cholinergic-specific.